A key input apparatus as typified by a keyboard in which a plurality of key tops is arranged is generally used as a device for inputting information such as text, numbers, symbols or the like in various electronic devices, such as mobile phones, portable information terminals such as PDAs, electronic dictionaries and notebook personal computers.
Conventionally, rubber dome keyboards in which rubber domes are provided directly below the key tops, for example, have been used as notebook personal computer keyboards. In a rubber dome keyboard, when the user presses down the key top, the rubber dome positioned directly below the key top is pressed down. Through this, an electrical connection is made in a membrane sheet circuit, and a signal corresponding to the key top pressed down by the user is input into the electronic device such as a notebook personal computer.
In recent years, much development that is focused on reducing the thickness of the keyboards accompanying progress in making electronic devices more compact and thinner. In order to make the above-described rubber dome keyboard thinner, making the thickness of the rubber domes thinner has been considered. However, when the thickness of the rubber domes is reduced, problems arise in that rubber dome buckling properties worsen and the click sensation given to the user declines. Consequently, there are limits to further progress in making rubber dome keyboards thinner.
As a key input apparatus targeting thinness, in the past an input apparatus has been proposed (see Patent Literature 1) that comprises a magnetoresistive effect element and a plurality of magnets provided on a substrate, a support body composed of an elastic material covering the magnetoresistive effect element and the magnets, and a ferromagnetic material embedded in the support body. In this input apparatus, a zero magnetic field region is formed on the substrate by alternating the N-poles and S-pole of the magnets, the magnetoresistive effect element is positioned within the zero magnetic field region on the substrate, and the support body is provided such that the ferromagnetic material is positioned directly over the magnetoresistive effect element. Furthermore, when the ferromagnetic material is displaced by operation of the support body, a change in the distribution of the magnetic field strength on the substrate is caused, and the resistance value of the magnetoresistive effect element changes in accordance with this change in the distribution of the magnetic field strength.
In addition, an input apparatus that uses a magnetism detection element and magnets has been proposed (see Patent Literature 2) that comprises two magnets provided on a substrate with a gap in between the two, an MR element provided on the substrate to be interposed between the two magnets, and a soft magnetic material provided on the MR element to be displaceable. In this input apparatus as well, the strength of the magnetic field emitted from the magnets changes depending on the displacement of the soft magnetic material, and through this the resistance value of the MR element changes.